Biosensors are devices for sensing and detecting biomolecules and operate on the basis of electronic, electrochemical, optical, and mechanical detection principles. Biosensors that include transistors are sensors that electrically sense charges, photons, and mechanical properties of bio-entities or biomolecules. The detection can be performed by detecting the bio-entities or biomolecules themselves, or through interaction and reaction between specified reactants and bio-entities/biomolecules. Such biosensors can be manufactured using semiconductor processes, can quickly convert electric signals, and can be easily applied to integrated circuits (ICs) and MEMS.
Additional circuitry is often required to read out signals from the biosensors and produce a quantifiable detection signal. Such circuitry can produce an analog output signal, or uses an analog-to-digital (ADC) converter to measure an analog signal from the biosensor and produces a digital detection signal. Analog signals are easily influenced by noise and the circuit components used with analog signals can consume a large portion of the total power of the biosensing system. Furthermore, integrating an ADC increases the chip cost and the die area.